I am not sure if this word has multiple meanings, but I am using it in an architectural context. Classical orders have distinctive columns with distinctive capitals. However, when I say each style also has a distinctive entablature, I am guessing many readers won't know what what the word entablature means (I didn't). So next to the word 'entablature', I would like to put in parentheses a synonym or very short phrase that defines the word 'entablature'.

Essentially, my question boils down to: What is a synonym or very-short phrase for the word 'entablature'?

There isn't really a synonym, but you can give a short list of example types rather than an alternate word (lintel, architrave, frieze, cornice, etc.) in the running text to give the reader a hint, and perhaps add a more complete definition in a footnote.

For someone who doesn't know what an entablature is, which I didn't before tonight, I think using cornice, frieze, and architrave is not going to help, although it would work for people who are familiar with architecture. Being largely ignorant of architecture myself, I'd describe it personally as an upper border or roof facing.